SE465815B - PROCEDURE FOR IMPROVING WOOD WITH ALKALILIGNIN - Google Patents

Abstract

A method for the impregnation of wood to prevent attack by harmful agents such as decay fungi or mould fungi and bacteria by the application of an aqueous solution of an alkali lignin modified into a water-soluble form. Impregnation takes place in two stages, these being an initial stage in which the aqueous solution containing the lignin still in its water-soluble form and with a pH not exceeding 10 is applied to the timber, and a second stage in which the lignin is fixed as a water-insoluble form by the application to the timber of a weakly acidic aqueous solution containing metal ions by the addition of metal salt.

Description

4ët5 yêellrlëgare object is to provide an impregnation process, which in addition to a protective effect provides a dimensional stabilizing effect on the impregnated wood without the need for any costly additions.

The object of the invention is achieved by carrying out the process with the features stated in claim 1.

The preparation used for impregnation in the process according to the invention consists in its active part mainly of lignin, suitably derived from the sulphate method for the production of pulp, so-called avlutslignin.

As is well known, such lignin is formed in large quantities in the manufacture of pulp according to the chemical method. This lignin is available in large quantities and at a price which makes it attractive in the present context.

In order for the lignin to be absorbed by the wood during the impregnation process, it should suitably be in the form of an aqueous solution. Due to its liquid form, it is suitable for use in the established methods, where the wood is introduced into the pressure chamber and supplied to the impregnation unit by overpressure. Water as a solvent is then of course suitable for use for cost reasons and cooperates with the moisture present in the wood.

In order for the lignin to obtain a water-soluble form, the same can e.g. carboxymethylase. The starting material is then suitably sulphate lignin, which is precipitated with acid at e.g. pH 9 from industrial effluent from sulphate boiling. The sulphate lignin is reacted in aqueous solution (10 hours, 90 ° C) with NaOH and monochloroacetic acid in a molar ratio of 1: 2: 1, the molecular weight of a C9 unit in the lignin being set to 200. The carboxymethylated lignin is precipitated with acid at pH approx. . 2 and is isolated by centrifugation. To obtain a purification, the lignin can then be dissolved in acetic acid and precipitated again.

The impregnation itself is suitably available according to the above-mentioned known method. The wood to be impregnated is placed in a pressure chamber, which is closed. Thereafter, the wood is subjected to vacuum, so that a large part of the air enclosed in its pores is removed. The impregnation solution is then added and pressurized, penetrating the wood. The wood that can be considered is primarily pine wood, but other softwood and also hardwood seem to be treatable. This step in the procedure and the appropriate data are shown in the attached examples, see especially example 1.

After the impregnation, a large part of the water will evaporate and the impregnating substance, lignin, remains. However, in its water-soluble form, it is sensitive to leaching and in this state the material could not be used, where it is primarily intended to be used, thus outdoors. The lignin must therefore be fixed by transferring it to a water-insoluble form. This can be done by C) 465 after the wood material in a second impregnation step is treated with an aqueous solution of aluminum sulphate, copper sulphate or a mixture of aluminum and copper sulphate. The fixing is carried out under pressure as shown in the examples. The advantage of using copper is that this metal even in small amounts provides a complementary rot protection. The combination of lignin and copper provides good resistance to white and brown rot as well as to soft rot and thinning bacteria from unsterile soil. It is also possible to carry out fixation by heat treatment, whereby cleavage of acetyl groups in the wood and chemical reaction between the wood substance and the lignin material, preferably in ammonium salt form, contributes to the lignin being transferred to water-insoluble form. The temperature of the heat treatment must be at least 80 ° C, preferably 110 ° C, in order for a good reaction to take place.

An important observation in connection with the invention is that the aqueous solution must be acidic or neutral, but not alkaline, or only slightly alkaline (pH max 10) in order to achieve a good result. By avoiding an excessively alkaline solution, the wood's own resistance to rot is affected to the least possible extent. On the other hand, the influence of the wood by an alkali means a certain swelling of the wood and thus improved penetration of the lignin into the cell wall. This in turn provides an improved impregnation effect. It is thus important to adjust the pH value, so that a good impregnation effect is obtained with a reasonable reduction in the wood's natural root resistance. The optimum pH value is in the range 6-10. The reduction of the natural resistance applies primarily to brown and soft rot. The reduction obtained even with the weakly alkaline solution can be compensated by means of copper addition, as shown below.

The fixing rig solution is added in the form of a slightly acidic solution, which improves the fixing effect by facilitating the chemical process, which converts the lignin to a water-insoluble form. This process requires a relatively large amount of metal ions and the amount increases with increasing amount of lignin during the impregnation. At commonly used lignin concentration, a larger amount of metal ions is required than is obtained by the copper required for said supplementary rot protection. Since copper has a higher price than aluminum, the fixing solution is therefore suitably based in part on salt of copper to the amount required for said supplementary rot protection, and on the remaining part on salt of aluminum for the required fixing. Instead of copper, zinc can be used. For said supplementary rot protection, it is required that the wood contains a balanced amount of copper in relation to the type of wood and the amount of lignin added, which can be limited to 1% calculated on dry wood. However, a reading of the tables shows that the rot resistance is also to some extent dependent on the pH value of the impregnation solution. In some cases, the impregnation treatment may focus on specific attack conditions. Thus, the requirements regarding rot resistance may differ in the case of timber which is intended for mounting above ground, in relation to timber which is intended to be immersed in soil. A higher lignin content provides increased dimensional stabilization of the wood. The smallest amount of copper needed to provide good complementary rot protection, the so-called threshold value, varies with the type of wood. Thus, hardwood generally needs to approximately double the amount that e.g. required for softwoods such as pine.

Example 1 Pine blocks were impregnated at 50 ° C with an aqueous solution of carboxy-methylated sulphate lignin (pH 7). Vacuum pressure impregnation was applied with a vacuum period of 30 minutes followed by a pressure period of 90 minutes at 1 MPa. After the impregnation, the wooden blocks had increased in weight to about 2.5 times the dry origin weight. Drying 'to (slightly) absorbent state so that fixing solution can penetrate (avoid time-consuming diffusion). After drying and weighing, the absorbed lignin content was determined to be about 15% by weight based on dry wood.

To obtain the impregnated lignin in a water-insoluble and non-leachable form, the lignin was fixed by treating the wood material in a second impregnation step with an aqueous solution of aluminum sulphate, copper sulphate or a mixture of aluminum and copper sulphate. The fixation was performed at 20 ° C and the length of the printing period was 60 minutes at about 1 MPa.

Untreated as well as treated wood was tested for resistance to white rot, brown rot and soft rot and thinning bacteria (unsterile soil).

Results of this rot test are reported in Table 1. Test no. 1 without fixation of the lignin showed a weight loss during water leaching corresponding to a leaching of about 90% of the impregnated lignin. The treatment is thus not sufficient, as the wood material must be used outdoors and exposed to moisture. Fixation with aluminum and / or copper sulphate gave a lignin leaching in water which was less than 1% of the amount of modified lignin added.

As can be seen from Table 1, impregnation and fixation with only aluminum sulphate (sample 2) | gives good resistance to white and brown rot, while the attack of mainly soft rot (unsterile soil) became relatively strong. Addition of small amounts of copper (0.3-0.4%) gave very good rot resistance (samples 3 and 4), probably due to a synergistic effect of the impregnation and fixation.

A treatment according to claim 1 also resulted in an increased dimensional stability. Tests according to American norm gave an initial dimensional stability of so% (samples 2-4).

J! 462 815 Example 2 Pine blocks were vacuum-impregnated with an aqueous solution of carboxymethylated sulphate lignin in ammonium ion form (pH about 9) followed by an impregnation with dilute copper salt solution to introduce copper ions into the wood material at a content of 0.2% Cu, giving supplementary rot protection with insufficient fixing effect.

Fixation of the water-soluble lignin to a water-insoluble form in the wood was then effected by heating the impregnated wood material to a temperature of 105-115 ° C for one hour, during which simultaneous drying took place.

Results of rot tests are reported in Table 2. The tests were performed in the same manner as in Example 1.

Example 3 Pine block wood blocks were impregnated according to the procedure given in Example 1 with lignixi solutions of varying concentration to give the levels of modified lignin given in Table 3 in the wood. The pH of the lignin solutions was either 7 or 9. Fixation was carried out with a solution of aluminum and copper salt or alternatively only copper salt so that the stated copper contents were obtained. All content indications apply to wooden blocks which, after fixing, have been water-leached for a week with repeated water change. Results of brown rot test (7 weeks exposure time) are shown in Table 3. (1,465,815 JGmoouQw fl- v fl ïw wo | mo Sm fl s-.Ö .Qmwuw fl m G35 nmšouß wwmm fl .Hm .w fi nm fl omww muu fi m fi mw ww m ë mw m. amu al vwwoë m .www .m fi mxw .wwwmnwum Pm fifl o w f cëwvwm Am .Am f oo fifi m wwwao fi ëomv mumncøun Gm ws fi xwmmwu Awwucmw f w mwmnownw fi NMV Sm f IW cm have .B al mcmë et al .m fi uwdoaxm AH woman 80 microns H6 + M§cmvß <m: w Amo iM m6 wOwøü tra mm QS mc . fi ^ womv ~ ë BN w: ï fi äâ - EH. m! .w. mm w. om 1 .. SPSSOM AN .cmE m .Éäw .Uno fi muwaa fl um muæuu fi w nå: æ .fi cwm mäömo w QQPwG <Sw .umw fi mn Utv uwøimmm fi å> .wuïwxwm uwnø fifl uoå kwonm H fl onmh ._ Jui- OO á.

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Claims (9)

465 last PATENT REQUIREMENTS Method for impregnating wood against pests, such as rot or mold and bacteria, by adding an aqueous solution of an alkali lignin modified to a water-soluble form, characterized in that the impregnation takes place in two steps, a first step in which the aqueous solution with the lignin still in water-soluble form and with a pH not exceeding 10 is added to the wood to be taken up by it, and a second step in which the lignin is fixed by transferring to a substantially water-insoluble form for retention in the wood via the action of the wood with its content of added lignin, which second step involves the addition of a weakly acidic aqueous solution containing metal ions by the addition of at least one metal salt. 2. Process according to claim 1, characterized in that the metal salt consists of aluminum, zinc or copper salt or a combination of these salts. 3. A method according to claim 2, characterized in that the salt consists partly of copper salt in such an amount that the amount of copper in relation to dry wood is substantially not higher than 1% and partly of another metal salt preferably aluminum salt to such an extent that the lignin is fixed by the combined action of these salts. A method according to claim 1, characterized in that the aqueous solution is added ammonium salt or sodium salt and that the second step for fixing the lignin in addition to the addition of the metal salt comprises heating the wood to a temperature of at least 80 °, preferably 10 ° C. 5. A method according to claim 4, characterized in that the wood is fed to copper, preferably by using a solution of one copper salt in the second step. 6. A method according to claim 4, characterized in that the wood is supplied with zinc, preferably by using a solution of a zinc salt in the second step. 7. A process according to any one of claims 1-6, characterized in that the lignin is modified to carboxylated alkaline lignin, preferably by oxidation and thereby obtained water-soluble form. / 0 465 815 Process according to any one of claims 1-6, characterized in that the lignin is modified to carboxyalkylated alkali lignin, preferably carboxyethylated and / or carboxyethylated alkali lignin to thereby obtain water-soluble form. 9. that the lignin modified to water-soluble form is further modified by Process according to claim 7 or 8, characterized by sulfonation.